In tropically located countries, like those in South America and Asia, mosquitoes are more than a simple nuisance, they are vectors of deadly diseases. Diseases like Dengue Haemorrhagic fever, Malaria, Yellow Fever, and various types of Encephalitis. Protecting ones self and family from these diseases is a premium concern of individuals in these areas. Devices that repel and kill mosquitoes abound in these places. There are 3 basic types of anti-mosquito devices, aerosol insecticides, coils, and electrical devices like mats and emanators.
Aerosols dispense oil or water based, insecticide containing droplets into the air which impact on the mosquito, delivering the insecticide and killing the insect. These droplets impact on mosquitoes and either repel them or kill them depending upon how many droplets the mosquito encounters. Aerosols are effective from a few minutes to 2 hours.
Coils are composed of pressed sawdust impregnated with a small amount of insecticide. The coil is lit with a match and begins to smolder slowly. As it smolders, the heat evaporates the insecticide into the air as a vapor where it quickly cools and forms micron sized droplets 2–5 μm in size.
Electrical devices like mats and emanators use electrical heat instead of smoldering sawdust. Mats are insecticide and a carrier or solvent impregnated into cotton linter that are placed on a small metallic heating plate which drives off the active ingredient into the air in the same manner as the coils. Mats can last from 4–13 hours.
Emanators work much the same way but they use a liquid reservoir which contains insecticide and a carrier solvent. The insecticide is carried up to the heating element by a wick, usually ceramic. Because the reservoirs are large, emanators can last up to 90 days.
Electrically powered flying insect killers, like other emanator devices have been growing in popularity for some time. Emanators are preferred over aerosols because of the convenience of long operation and their odorless operation.
They are safer than coils, with their drastically reduced fire risk, and cleaner because there are no messy ashes or smoke to deal with. They cost less, in day to day usage, than mats or coils. They are more modern, upscale products, preferred over seemingly low-tech coils and aerosols.
But even the traditional emanator has its problems. Emanators require heat, drawing a fair amount of power and normally running at a dangerously high temperature. Burns are common with these products and there is always a risk of fire where there is excessive high heat. Emanators must be plugged into a wall socket, meaning placement is limited. Emanators must be operating at full temperature to drive off mosquitoes, and they usually take quite a while to heat up. Consumers may have to wait for an hour after turning on their device before seeing any mosquito reduction. Because of the heat involved, emanator devices often have problems with insecticide vapors condensing on the plastic casing, or walls immediately adjacent to the device. Because different insecticides evaporate off at different temperatures, the heater temperature, active ingredient evaporation temperature and solvent evaporation temperature must be precisely matched.
FIG. 1A is a representative perspective view of a liquid emanator device 100 of the prior art. FIG. 1B is a representative partial cutaway view of a liquid emanator device of the prior art. Liquid emanator devices 100 are the most recent stage in the evolution of products for vaporizing anti-mosquito and other insect formulations. Typically, these devices 100 comprise a reservoir 102 containing an insecticidal solution, formulation or compound 104. The insecticidal solution 104 is typically a hydrocarbon solvent mixture with a dissolved pyrethroid insecticide. A wick 106, generally made of a carbon or ceramic-based material, is inserted into the insecticidal solution 104 at a liquid end 108. The other, non-immersed end 110 of the wick 106 is positioned within a heater element 112, similar to those found in mat heaters, but usually annular in shape to surround the wick 106.
A housing 120 couples the assembly together. Electrical contacts 122 and switch means 124 provide a source of electrical energy to the resistive heating element 112. As the solvent and insecticide solution 104 is vaporized from the heated area, solution moves up the wick 106 by capillary action. The major advantage of this type of device over other vaporizers is that it does not produce any smoke compared to coils, and it lasts longer than one night, compared to typical coils and mats.
Liquid emanator devices 100 provide flexibility in the way the devices 100 are used over time. They can be used in continuous operation, only during the day, only during the night, or as needed. Overall duration varies typically between 30 to 60 nights, at up to 10 hours per night.
Another advantage of the liquid emanator devices 100 of the prior art is that they allow use by a consumer without any direct contact with the insecticidal solution 104. The use of a semi-clear plastic reservoir bottle 102 provides a visible indication of when the formulation is exhausted. The reservoir portion 102 can be replaceable, refillable, detachable or permanently or otherwise coupled to the system 100.
FIG. 1C is a representative section view of a resistive heating element-type emanator device 150 of the prior art. In this type of device 150, the cap portion 152 is filled with a liquid or other form of insecticidal solution 154. The cap portion 152 couples securely and directly to the high thermal conducting metal surface 156 covering the PTC-type heating element 158. Any of different plug 160 options are available, and a housing portion 162 retains the assembly together.
In operation, electrical current directed through the PTC-type heating element 158 causes an increase in surface temperature of the high thermal conducting metal surface 156. As this heat is transferred to the cap portion 152 containing the insecticidal compound 154, the compound 154 is evaporated and driven out of vents 164 in the housing 162. Metering means 166. Such as adjustable vent portions, flaps, cover plates, passive and/or dynamic heat sink, or height adjustment mechanism, serves to control the degree, amount, rate or other parameter of vaporization of insecticidal compound 154.
Atomization of liquids can be achieved in many ways. U.S. Pat. No. 4,532,530, issued Jul. 30, 1985 to Hawkins teaches a bubble-jet printing device. U.S. Pat. No. 5,646,660, issued Jul. 8, 1997 to Murray teaches a printer ink cartridge with drive logic integrated circuit. Generally speaking, ink jet printing systems can be divided into two types; viz, continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, so that the stream breaks up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is to not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. The major components of one type of drop-on demand system are an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the systems ability to produce high quality copies. The drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
The bubble jet concept is the other drop-on-demand system, and it is very powerful because it produces high velocity droplets and allows very close spacing of nozzles. The major components of the second type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle.
As the name suggests, printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. The process is ready to start all over again as soon as hydrodynamic motion of the ink stops. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the “bubble jet” system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous steam counterparts and yet have substantially the same high speed printing capability.